Gear reduction wheel mechanisms have been made in a variety of structures. One form of vehicle wheel mechanism, as in U.S. Pat. No. 2,899,055, provides an electric motor disposed within the wheel and then a compound gear set inboard of the electric motor and connected to drive the wheel. With large wheels for earth moving equipment wherein the wheel may weigh several tons, it becomes extremely time-consuming to service the gear reduction mechanisms because the wheels and tires must be removed, the electric motor removed, and finally the gear set is made available.
Some such wheel mechanisms have been provided with a motor inboard and a gear mechanism outboard generally within the plane of the wheel. The typical construction of such wheel mechanism, as in U.S. Pat. No. 3,055,448, is one wherein the axially outboard gear case wall is rotating and rotates with the last stage planet carrier of a planetary gear set. In recent years, safety has been of greater concern, including the ability to stop large trucks which might be 100 to 300 tons load carrying capacity. The typical braking for such trucks is dynamic retarding, with the electric motor acting as a generator to generate electrical power which is dissipated in resistor grids. On long downgrades, however, the resistor grids may overheat and some friction brake mechanism is highly desirable and is becoming mandatory in some locations. Also, it is necessary to use friction brakes to bring the vehicle to a dead stop, since some considerable forward speed is required to create a retarding force using dynamic braking. Disc brakes have been used on such wheel mechanisms, but in many cases they are motor speed brakes as distinguished from wheel speed brakes. This is the type shown in U.S. Pat. No. 3,897,843.
Another construction, such as in U.S. Pat. No. 2,258,328, is one wherein the brake is between the motor and the gears, but this has the deficiency of needing to take the wheel and tire off to service the brake. Where the wheels are large units, for example where one entire wheel mechanism might weigh 6 tons for a vehicle having a load hauling capacity of 150 tons, it might take as much as an eight-hour shift for men with proper equipment to take a wheel apart for servicing of the internal brake.
Another type of motorized wheel achieved a nonrotating axially outboard gear case wall together with a planetary gear final drive. This is the type shown in U.S. Pat. No. 3,090,456. However, in such construction, the output from the final planetary gear was from the planet carrier and such output was inwardly to a small diameter sleeve, then axially outwardly, and then radially outwardly to the wheel. Accordingly, in such construction, there was no nonrotating gear case wall which was radially inboard of the output to the wheel.
Still another construction of wheel mechanism, as in U.S. Pat. No. 3,812,928, was one wherein the gear case outer wall was stationary, and there was a planetary final drive to the wheel; however, this required an inside-out motor with a stationary shaft which was large in diameter in order to be able to carry the weight of the vehicle on such long cantilevered, fixed shaft.
The deficiencies of the prior art construction then brought about the question of how to achieve a wheel speed brake which was axially outboard of all of the rest of the mechanisms in a vehicle wheel mechanism and with the planetary gear mechanism next available, immediately inboard of the brake.